source: vbox/trunk/src/libs/liblzma-5.8.1/common/index_encoder.c@ 108993

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       index_encoder.c
/// \brief      Encodes the Index field
//
//  Author:     Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#include "index_encoder.h"
#include "index.h"
#include "check.h"


typedef struct {
        enum {
                SEQ_INDICATOR,
                SEQ_COUNT,
                SEQ_UNPADDED,
                SEQ_UNCOMPRESSED,
                SEQ_NEXT,
                SEQ_PADDING,
                SEQ_CRC32,
        } sequence;

        /// Index being encoded
        const lzma_index *index;

        /// Iterator for the Index being encoded
        lzma_index_iter iter;

        /// Position in integers
        size_t pos;

        /// CRC32 of the List of Records field
        uint32_t crc32;
} lzma_index_coder;


static lzma_ret
index_encode(void *coder_ptr,
                const lzma_allocator *allocator lzma_attribute((__unused__)),
                const uint8_t *restrict in lzma_attribute((__unused__)),
                size_t *restrict in_pos lzma_attribute((__unused__)),
                size_t in_size lzma_attribute((__unused__)),
                uint8_t *restrict out, size_t *restrict out_pos,
                size_t out_size,
                lzma_action action lzma_attribute((__unused__)))
{
        lzma_index_coder *coder = coder_ptr;

        // Position where to start calculating CRC32. The idea is that we
        // need to call lzma_crc32() only once per call to index_encode().
        const size_t out_start = *out_pos;

        // Return value to use if we return at the end of this function.
        // We use "goto out" to jump out of the while-switch construct
        // instead of returning directly, because that way we don't need
        // to copypaste the lzma_crc32() call to many places.
        lzma_ret ret = LZMA_OK;

        while (*out_pos < out_size)
        switch (coder->sequence) {
        case SEQ_INDICATOR:
                out[*out_pos] = INDEX_INDICATOR;
                ++*out_pos;
                coder->sequence = SEQ_COUNT;
                break;

        case SEQ_COUNT: {
                const lzma_vli count = lzma_index_block_count(coder->index);
                ret = lzma_vli_encode(count, &coder->pos,
                                out, out_pos, out_size);
                if (ret != LZMA_STREAM_END)
                        goto out;

                ret = LZMA_OK;
                coder->pos = 0;
                coder->sequence = SEQ_NEXT;
                break;
        }

        case SEQ_NEXT:
                if (lzma_index_iter_next(
                                &coder->iter, LZMA_INDEX_ITER_BLOCK)) {
                        // Get the size of the Index Padding field.
                        coder->pos = lzma_index_padding_size(coder->index);
                        assert(coder->pos <= 3);
                        coder->sequence = SEQ_PADDING;
                        break;
                }

                coder->sequence = SEQ_UNPADDED;
                FALLTHROUGH;

        case SEQ_UNPADDED:
        case SEQ_UNCOMPRESSED: {
                const lzma_vli size = coder->sequence == SEQ_UNPADDED
                                ? coder->iter.block.unpadded_size
                                : coder->iter.block.uncompressed_size;

                ret = lzma_vli_encode(size, &coder->pos,
                                out, out_pos, out_size);
                if (ret != LZMA_STREAM_END)
                        goto out;

                ret = LZMA_OK;
                coder->pos = 0;

                // Advance to SEQ_UNCOMPRESSED or SEQ_NEXT.
                ++coder->sequence;
                break;
        }

        case SEQ_PADDING:
                if (coder->pos > 0) {
                        --coder->pos;
                        out[(*out_pos)++] = 0x00;
                        break;
                }

                // Finish the CRC32 calculation.
                coder->crc32 = lzma_crc32(out + out_start,
                                *out_pos - out_start, coder->crc32);

                coder->sequence = SEQ_CRC32;
                FALLTHROUGH;

        case SEQ_CRC32:
                // We don't use the main loop, because we don't want
                // coder->crc32 to be touched anymore.
                do {
                        if (*out_pos == out_size)
                                return LZMA_OK;

                        out[*out_pos] = (coder->crc32 >> (coder->pos * 8))
                                        & 0xFF;
                        ++*out_pos;

                } while (++coder->pos < 4);

                return LZMA_STREAM_END;

        default:
                assert(0);
                return LZMA_PROG_ERROR;
        }

out:
        // Update the CRC32.
        //
        // Avoid null pointer + 0 (undefined behavior) in "out + out_start".
        // In such a case we had no input and thus out_used == 0.
        {
                const size_t out_used = *out_pos - out_start;
                if (out_used > 0)
                        coder->crc32 = lzma_crc32(out + out_start,
                                        out_used, coder->crc32);
        }

        return ret;
}


static void
index_encoder_end(void *coder, const lzma_allocator *allocator)
{
        lzma_free(coder, allocator);
        return;
}


static void
index_encoder_reset(lzma_index_coder *coder, const lzma_index *i)
{
        lzma_index_iter_init(&coder->iter, i);

        coder->sequence = SEQ_INDICATOR;
        coder->index = i;
        coder->pos = 0;
        coder->crc32 = 0;

        return;
}


extern lzma_ret
lzma_index_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
                const lzma_index *i)
{
        lzma_next_coder_init(&lzma_index_encoder_init, next, allocator);

        if (i == NULL)
                return LZMA_PROG_ERROR;

        if (next->coder == NULL) {
                next->coder = lzma_alloc(sizeof(lzma_index_coder), allocator);
                if (next->coder == NULL)
                        return LZMA_MEM_ERROR;

                next->code = &index_encode;
                next->end = &index_encoder_end;
        }

        index_encoder_reset(next->coder, i);

        return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_encoder(lzma_stream *strm, const lzma_index *i)
{
        lzma_next_strm_init(lzma_index_encoder_init, strm, i);

        strm->internal->supported_actions[LZMA_RUN] = true;
        strm->internal->supported_actions[LZMA_FINISH] = true;

        return LZMA_OK;
}


extern LZMA_API(lzma_ret)
lzma_index_buffer_encode(const lzma_index *i,
                uint8_t *out, size_t *out_pos, size_t out_size)
{
        // Validate the arguments.
        if (i == NULL || out == NULL || out_pos == NULL || *out_pos > out_size)
                return LZMA_PROG_ERROR;

        // Don't try to encode if there's not enough output space.
        if (out_size - *out_pos < lzma_index_size(i))
                return LZMA_BUF_ERROR;

        // The Index encoder needs just one small data structure so we can
        // allocate it on stack.
        lzma_index_coder coder;
        index_encoder_reset(&coder, i);

        // Do the actual encoding. This should never fail, but store
        // the original *out_pos just in case.
        const size_t out_start = *out_pos;
        lzma_ret ret = index_encode(&coder, NULL, NULL, NULL, 0,
                        out, out_pos, out_size, LZMA_RUN);

        if (ret == LZMA_STREAM_END) {
                ret = LZMA_OK;
        } else {
                // We should never get here, but just in case, restore the
                // output position and set the error accordingly if something
                // goes wrong and debugging isn't enabled.
                assert(0);
                *out_pos = out_start;
                ret = LZMA_PROG_ERROR;
        }

        return ret;
}